Supported Molecular Catalysts: Synthesis, In-Situ Characterization and Performance

Abstract

Objectives:The objectives of our work are: (i) to create solid catalysts with active sites that can function in a cooperative manner to enhance reactivity and selectivity, and (ii) to prepare solid catalysts that can perform multiple reactions in a network that in some cases would not be possible in solution due to the incompatibilities of the various catalytic entities (for example an acid and a base). Summary of Work:We began this project with the observation that two sulfonic acids placed in close proximity of each other on a mesoporous solid (SBA-15) appeared to provide enhanced reactivity and selectivity over what was achievable with individual sulfonic acid sites on the solid or in solution for the condensation reaction of acetone and phenol to bisphenol A (Dufaud and Davis, J. Am. Chem. Soc. 2003, 125, 9403-9413). We carried out extensive homogeneous reactions using combinations of thiols and sulfonic acids to test the nature of the cooperative effect that was observed to investigate if the cooperativity was caused by sulfonic acid/sulfonic acid interactions or thiol/sulfonic acid interactions [1]. Next, we created a series of materials to test the effect of distance between the two functional groups. The methodology is illustrated below. The catalytic data show that the further the thiol is placed from the acid, the slower the reaction kinetics [4]. Thus, the thiol should be as close to the acid center as possible. In order to create a strong acid/thiol combination, we developed a better synthetic strategy as illustrated below.